Select (and unselect) a field by clicking on it with the left mouse button.
You can select multiple fields by clicking on them with the left mouse button while holding the shift key.
You can move fields by dragging and dropping selected fields while holding the left mouse button.
Resize fields by dragging one of the corners of the selected field.
You can edit field attributes by double clicking on the field.
Apply your changes by closing the dialog (with X)
Selecting "Delete Field" removes the field from the label.
Selecting "Show Field List" from the "Fields" menu opens the field list.
Reorder the print order of the fields with drag and drop.
You can change the field attributes by double clicking on a field.
You can change the "Label and Page Attributes" by double clicking on them.